Personal washing bars are constantly moving toward milder formulations that ultimately will provide some enhanced skin care, for example, minimizing levels of skin irritation and enhancing moisturization. It is desirable to have a bar composition that carries a significant amount of emollient oily liquid that provides positive sensory cues to many consumers. To properly process such a bar composition, cast-melt is the preferred technique.
It is a challenge to find an economical bulk chemical which can function as a bar filler/binder that enhances skin mildness or moisturization, promotes bar lather performance and facilitates bar processing. For example, solid polyalkylene glycols (e.g., polyethylene glycols (PEG) having molecular weight above 2000) are effective bar structurants and they do not defoam. However, in comparison to a PEG having a lower molecular weight, they provide much less oily skin feel which signals moisturization to many consumers, and they are less readily miscible with long chain fatty acid soaps that are used as gelling agents in the subject invention. Solid fatty acids, on the other hand, can effectively structure bar but tend to defoam. Paraffin waxes defoam if included in a bar at relatively high levels (i.e., greater than 25% wt. total composition), especially in the presence of hydrophobic emollient oils.
In the subject invention, applicants have formulated relatively high levels of low molecular weight polyalkylene glycols (e.g., polyethylene glycol having molecular weight of 300 to below 1500, preferably about 350 to 1450, more preferably 350 to 1400, more preferably 350 to 1300) in a synthetic detergent bar using the cast melt technology. In-vivo and in-vitro data showed that, only at high levels of addition (polyethylene glycol to anionic weight ratio at 1:1 and above) do these low MW PEGs significantly mitigate the irritation potential of commonly used anionic surfactants. Unlike solid PEGs with molecular weight greater than 1500, the low molecular weight PEGs are more readily miscible with long chain fatty acid soaps that are the gelling agents of this invention, and therefore are a significant component of the immobilized liquid fraction of these bars. It is this liquid fraction that readily dissolves upon use providing the benefits of enhanced skin feel, mildness and lather. As an additional benefit, the low molecular weight PEGs enhance desired lather properties to a skin cleanser.
Thus using high levels of these relatively low molecular weight materials, applicants were able to obtain bars which simultaneously (1) provided desired user and processing properties (2) lathered well and (3) were less irritating.
The use of polyalkylene glycol (e.g., polyethylene glycol) in personal washing bar compositions is not itself new.
U.S. Pat. No. 3,312,627, to D. Hooker, for example, teaches a bar composition containing 30-70% polyethylene glycol (PEG) as bar structurant for a nonionic formulation basically free of anionic detergents. The PEG used in this invention has a molecular weight above 4000 Dalton, which is significantly higher than the MW claimed for the PEGs applied in the subject invention (less than 1500, preferably greater than 300 to about 1450 and below). In contrast to the subject invention, the referred patent used significantly higher level of high MW PEG in total bar composition. Further, the PEG/anionic surfactant ratio is not important in this patent since it refers to a primarily nonionic formulation.
World Patent Application No. 93/07245 to F. Moran, B. O'Briain and D. Moran (assigned to NEPHIN) teaches a shampoo bar composition containing 12-20% synthetic detergents and 70-80% PEGs with molecular weight between 5000 and 10,000. An embodiment of the invention includes a softening PEG with molecular weight between 100 and 800 (preferably 1-8% wt. total composition). In contrast to the subject invention, the referred patent application used a significant level (70-80%) of high MW PEGs in total bar composition. The referred patent used significantly less amount of low MW PEG than used in the subject invention.
In applicant's copending U.S. Ser. No. 08/594,363, Continuation of U.S. Ser. No. 08/213,287, entitled "Synthetic Detergent Bar and Manufacture Thereof", to J. Chambers et al., there is taught a bar containing 10-60% synthetic surfactants and 10-60% PEG as structurant. The PEG used has a range of melting temperatures between 40.degree. C. and 100.degree. C., and a range of molecular weight between 1500 and 10,000. This molecular weight makes PEG a solid at room temperature. The PEG molecular weight used is above that claimed (less than 1500, preferably about greater than 300 to about 1450 and below) by the subject invention. Also the referred patent application does not teach PEG/anionic ratio of at least 1:1 that is relevant to the mildness enhancement, a criticality of the subject invention.
U.S. Pat. No. 5,520,840 to M. Massaro et al. teaches a skin cleansing bar composition containing 10-60% of synthetic surfactant, 10-60% water soluble structurant (e.g., PEG) with having a range of melting points between 40.degree. C. and 100.degree. C., and 1-25% water soluble starch such as maltodextrin. Again, the molecular weight of the PEGs used (i.e., above 1500) is above that claimed for the subject invention. Also the referred patent application does not teach a PEG/anionic ratio of at least 1:1 that is relevant to the mildness enhancement, a criticality of the subject invention.
U.S. Pat. No. 2,287,484 to Lundberg teaches a bar made by a closed die molding technique which comprises 35-70% of anionic synthetic surfactant and 22-50% fatty acid. The bar also may contain up to 10% ethylene and di-ethylene glycols as additives. As found by the subject invention, the ethylene and di-ethylene glycols are not as effective as low MW PEGs (MW above 300) in reducing the skin irritation of anionic surfactants. Also the referred patent does not teach a PEG/anionic surfactant weight ratio of at least 1:1 that is relevant to the mildness enhancement, a criticality of the subject invention.
Applicants' copending application Ser. No. 08/662,394, filed Jun. 12, 1996 teaches a mild bar composition containing 10-60% synthetic detergents, 10-50% high molecular weight PEG with melting point above 40.degree. C. and 0.1 to 10% low molecular weight PEG (melting point below 40.degree. C.) as processing aid. The application claims the use of relatively low levels of low MW PEG as a lubricant to aid the extrusion process. This is significantly different from the art of the subject invention, which formulated relatively high levels of low MW PEG (e.g., &gt;10% wt. total composition) into a bar as a moisturizer. Also the referred patent application did not specify the PEG/anionic surfactant weight ratio, which is a criticality of the subject invention to achieve superior skin mildness.
U.S. Pat. Nos. 5,262,079 and 5,227,086 to M. Kacher, J. Taneri, D. Quiram, D. Schmidt and M. Evans teach a framed cleansing bar composition containing 5-50% of a mixture of free and neutralized monocarboxylic acid, 15-65% synthetic anionic and nonionic bar firmness aid and 15-55% water. The bar firmness aid consists of 5-50% synthetic surfactants and 0-40% polyethylene glycol or polypropylene glycol with MW ranging from approximately 44 to 10,000 Dalton. The referred patents do not teach or suggest use of PEGS with MW between 400 and 1500 with specific PEG/anionic surfactant weight ratios to achieve both enhanced cast-melt processibility and mildness enhancement. Further, to obtain the desired bar user properties (i.e., mush and hardness) the applicants of the subject invention include only 2-10% wt. water in the bar compositions claimed, which is significantly below the 15-55% water claimed by the referred patents.
Finally, applicants are concurrently filing an application entitled "Pourable Cast Melt Bar Compositions Comprising Low Levels of Water and Minimum Ratios of Polyol to Water". The subject invention is made by the same cast melt methodology. However, the related application is not directed to specific compositions wherein high levels of polyalkylene glycol with molecular weight between 400 and 1,500 are used and ratio of polyalkylene glycol to anionic surfactant is at least 1:1.